Cell Theory and Discoveries

Study Notes

Robert Hooke, an English scientist, discovered cells in 1665 while examining a thin slice of cork.
- He described the cells as tiny boxes or a honeycomb.
- He believed cells only existed in plants and fungi.
Anton van Leeuwenhoek, using a handmade microscope in 1673, observed pond scum and discovered single-celled organisms.
- He called them "animalcules".
- He also observed blood cells from various animals, including fish, birds, frogs, dogs, and humans, establishing that cells exist in animals as well as plants.

Between the Hooke/Leeuwenhoek discoveries and the mid-19th century, there was minimal progress in cell research due to the widespread belief in Spontaneous Generation.
- This theory proposed the spontaneous creation of living organisms from non-living matter.
- Examples included the belief that mice could arise from dirty clothes or corn husks, and maggots from rotting meat.
Louis Pasteur conclusively disproved Spontaneous Generation in the 19th century.

Matthias Schleiden, a German botanist, observed various plant samples under a microscope in 1838.
- He concluded that all plant parts are made of cells, implying that plants are composed of cells.
Theodor Schwann, a German physiologist and close friend of Schleiden, stated in 1839 that all animal tissues are composed of cells.
Rudolf Virchow, a German physician, after extensive study of cellular pathology in 1858, concluded that cells must arise from preexisting cells.

All organisms are composed of one or more cells (Schleiden & Schwann, 1838-39).
The cell is the basic unit of life in all living things (Schleiden & Schwann, 1838-39).
All cells are produced by the division of preexisting cells (Virchow, 1858).

The cell contains hereditary information (DNA) which is passed on from cell to cell during cell division.
All cells are basically the same in chemical composition and metabolic activities.
All basic chemical and physiological functions are carried out inside the cells (movement, digestion, etc.).
Cell activity depends on the activities of sub-cellular structures within the cell (organelles, nucleus, plasma membrane).

A cell is the basic unit of living matter in all organisms, consisting of protoplasm enclosed within a cell membrane.
It is the fundamental unit of life.

Prokaryotic Cell
- Pro = before, karyon = kernel (referring to the nucleus).
- Cells without a true nucleus and membrane-bound organelles.
- Domains Bacteria and Archaea.
Eukaryotic Cells
- Eu = true, karyon = kernel (referring to the nucleus).
- A cell with a true nucleus and membrane-bound organelles.
- Domain Eukarya (protists, plants, fungi, and animals).

Both possess a selective barrier called the plasma membrane.
Both contain a semifluid, jellylike substance called the cytosol where subcellular components are suspended.
Both have chromosomes containing genes in the form of DNA.
Both have ribosomes, tiny complexes that make proteins based on the instructions carried by genes (DNA).